Polymer-monomer nematic mixtures

It is not necessary to carry out synthesis, if the triggering photochromic compound has good affinity to the polymer matrix. A mixture of the polyacrylate with BMAB which exhibits an excellent function as trigger is equally photoresponsive. While the monomer model compound (i.e. the acrylate before polymerization) does not provide a liquid crystalline phase, the polymer shows a clear nematic - isotropic transition at ca. 61 °C and the glass transition temperature at 24 °C as shown in Fig. 4. Tj j depends very much on the length of the alkyl spacer. In comparison with the... 

A phase diagram for a mesogenic side chain polymer and a related monomer is illustrated in Figure 7.3 (4,5). Note that the monomer by itself crystallizes. The nematic mixture clears in the temperature range of 360 to 370 K. 

MACROMOLECULAR ORDER AND CONFORMATION IN THE SOLID AND NEMATIC PHASES OF SEMI-RIGID POLYMERS AND POLYMER-MONOMER MIXTURES—NMR STUDY... 

One alternative approach is to use photoisomerisable chiral compounds where the E and Z isomers have different helical twisting powers, e.g. menthone derivatives. By incorporating co-polymers, prepared from menthone containing monomers and cyano esters (5.5), as dopants into nematic LC mixtures materials, e.g. a mixture of cyanobiphenyls and cyanoterphenyls (E7 available from Merck), colour change can be effected by irradiating with UV light (365 nm). The colour obtained is dependent... 

Fig. 13. Temperature dependence of the absorption E of the polymer/dye mixture M3 (refer to Table 4) (k = 430 nm, c = 0.5 mol % dye, related to the monomer unit of the polymer, d = 10 pm, E and E are the absorption parallel and perpendicular to the director of the nematic phase,...

In another study (Urbas et al., 2004b), the formulation of the mixture is different. It contains 35% of a nematic LC (E7) to which 3.5% of the LC azobenzene dopant (4-butyl-4-methyoxy-azobenzene) is added, with the rest being photopolymerizable monomer syrup. With such a formulation, polymerization is known to result in PDLC, in which phase-separated LC droplets are dispersed in the polymer matrix. When the photosensitive reactive mixture filled in an... 

LCDs [33]. Figure 9.7 shows the schematic structure and operating principles of the LC gel-based transflective LCD. The device is composed of an LC gel cell, two quarter-wave films, a transflector, a polarizer, and a backlight. The cell was filled with homogeneously aligned nematic LC and monomer mixture. After UV-induced polymerization, polymer networks are formed and the LC molecules are eonfined within the polymer networks. 

Nematic photo-crosslinkable polymers [108] and reactive monomer mixtures [109] can be easily oriented in a magnetic field. Due to their diamagnetism the mesogens usually orient parallel to the magnetic field in the LC phase. 

The monomer BMBB-6 (4 4-bis- 4-[6-(methacryloyloxy)-hexyloxy] benzoate - ,I biphenylene) and very small amounts of photoinitiator BME were mixed with 5CB to perform a study of the polymer network-induced birefringence in the isotropic phase of a nematic liquid crystal. Mixtures of 5CB in the nematic phase with 1, 2, 2.5, 3, and 4 wt.% of monomer were filled into planar cells and irradiated by UV light (4 W/cm ) at constant ambient temperature for 1 hour. 

The technique has also been used to study the dynamic behaviour of a polymer-dispersed liquid crystal subjected to an electric field [18]. The liquid polymer used was the commercially available nematic liquid crystal mixture E7, which contains four nitrile and ethyl substituted bi- and tri-phenyls. It was blended with a polymer precursor consisting of a mixture of an acrylate monomer, an acrylate oligomer and a UV curing agent. The 2D correlation analysis showed that the rigid core of the liquid crystal molecules re-orients as a unit, and suggests that the polymer side chains existing in the interface between the polymer and the liquid crystals may re-orient in phase with the liquid crystal re-orientation by interaction with the liquid cryst molecules. 

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